Compensated flat directional coupler

ABSTRACT

A compensated flat directional coupler includes a main branch carrying an electrical signal and a coupled branch carrying a coupled electrical signal responsive to the signal on the main branch. The coupled branch includes an auxiliary compensating network in the output portion of the coupled branch. The auxiliary compensating network couples to the coupled branch and is substantially isolated from the main branch. The auxiliary compensating network is substantially independent of the coupling between the main and coupled branch. The auxiliary coupling network renders the ratio of coupled output signal to the main branch output signal substantially independent of input signal frequency variation.



1. A coupled line compensating network for use with a TEM mode firsttransmission line coupler operative over a frequency range embracing apredetermined center frequency, said first coupler including meansdefining input, main output and coupler output ports and means definingmain and coupled branches, said main branch being arranged for carryingan electrical signal, said coupled branch being arranged for carrying acoupled signal in response to the signal carried by said main branch,said coupled line compensating network including means defining a seriesconductor having two ends for connection by one of said ends to saidcoupler output port for carrying said coupled signal to said other end,means defining at least one auxiliary branch coacting with said seriesbranch for establishing a coupling coefficient therebetween k2 andsubstantially isolated from said main branch for rendering the ratio ofsaid coupled signal to said signal on said main branch substantiallyinsensitive to frequency variation, said coefficient k2 being defined bythe following equation: k22 (1/1+sin theta e) wherein theta e definesthe band edge of said frequency range.
 2. A compensating networkaccording to claim 1 and further comprising, said first coupler, andmeans connecting said first coupler to said series branch to provide acompensatEd flat directional coupler, said first coupler comprisingcoupled lines characterized by a coupling coefficient k1 defined by:wherein K is the midband coupling of a compensated flat directionalcoupler comprising said first coupler and said compensating network
 3. Acompensated flat directional coupler according to claim 2 including atleast two of said auxiliary branches coacting with said series brancheach for a length corresponding substantially to an odd multiple ofquarter wavelengths at said center frequency of said first coupler.
 4. Acompensated flat directional coupler according to claim 3 comprising twoof said auxiliary branches coacting with said series branch and coupledthereto each for a length corresponding substantially to one quarterwavelength at said center frequency.
 5. A compensated flat directionalcoupler according to claim 4 wherein said first coupler comprises asingle section coupled transmission line coupler.
 6. A compensated flatdirectional coupler according to claim 2 wherein said first couplerincludes means defining a multiple section transmission line coupler andat least two of said auxiliary branches coact with said series branch todefine multiple section transmission line couplers.
 8. A compensatedflat directional coupler according to claim 3 wherein said first couplercomprises a single section coupled transmission line coupler and saidauxiliary branches coact with said series branch to define multiplesection transmission line couplers.
 8. A compensated flat directionalaccording to claim 3 wherein the coupling coefficient achieved by eachof said auxiliary branches coacting with said series branch aresubstantially equal to one another.
 9. A compensated flat directionalcoupler according to claim 3 comprising an even number of said auxiliarybranches coacting with said series branch each for a lengthcorresponding substantially to an odd multiple of quarter wavelengths atsaid center frequency of said first coupler.